Replace `build/manifest.json` make target with `make build`

`make build` is a more obvious name for a command that creates a
production build of the client. It also resolves an issue that `make
build/manifest.json` did nothing if `node_modules/` was up to date but
other dependencies had changed.

Makefile

@@ -5,6 +5,7 @@ default: help
 help:
 	@echo "make help              Show this help message"
 	@echo "make dev               Run the app in the development server"
+	@echo "make build             Create a production build of the client"
 	@echo "make lint              Run the code linter(s) and print any warnings"
 	@echo "make checkformatting   Check code formatting"
 	@echo "make format            Automatically format code"
@@ -69,7 +70,8 @@ sure: checkformatting lint test
 python:
 	@./bin/install-python
 
-build/manifest.json: node_modules/.uptodate
+.PHONY: build
+build: node_modules/.uptodate
 	yarn run build
 
 node_modules/.uptodate: package.json yarn.lock

package.json

@@ -123,6 +123,6 @@
     "test": "gulp test",
     "typecheck": "tsc --build src/tsconfig.json",
     "report-coverage": "codecov -f coverage/coverage-final.json",
-    "version": "make clean build/manifest.json"
+    "version": "make clean build"
   }
 }